(1) Field of the Invention
The invention relates to the manufacture of integrated circuit (IC) devices, and more particularly to the notching-free metal interconnection fabrication.
(2) Description of the Prior Art
In the conventional method of manufacturing IC devices, the making of metal interconnection is that aluminum is first formed by sputtering in a high vacuum chamber, then the metal interconnection line is then patterned by photolithography and etching techniques. However, the rough topography of the field oxide layer causes light reflection (see U.S. Pat. No. 5,406,373 to Kamon, the entire disclosure of which is herein incorporated by reference) which creates a photoresist notching phenomenon during the exposure step in the manufacturing process. Please refer to FIG. 1, which illustrates how photoresist notching happens. There is shown a partially completed IC device structure which comprises a silicon wafer 2, field oxide regions 4, an oxide layer 6, a metal layer 8, and a photoresist layer 10. When parallel incident radiation (light) 12 hits the rough field oxide regions 4 during exposure, some of the reflected light is directly scattered back to the bottom of the photoresist layer 10 or first scattered to metal layer then back to the bottom of the photoresist layer 10. These photoresist regions 10A thus become undesirably exposed and this causes the linear dimension of the photoresist to become narrower than originally designed. This photoresist notching problem causes the metal interconnection line 10 to become narrower also and this adversely influences the performance and yield of IC devices.
To prevent the metal line notching problem resulting from a highly reflective underlayer and/or a serious wafer topography, several approaches have been taken. The most commonly used methods is to apply an anti-reflection coating (such as TiN or amorphous silicon) on the surface of metal layer.
However, there are several drawbacks for using TiN or amorphous silicon as anti-reflection coating. First, it needs to different sputtering chambers to deposit this doublelayer structure that takes longer process time and thus increases the production cost. Second, there are plenty small particles produced during the TiN or amorphous silicon sputtering that causes chamber cleaning and maintenance more often. Third, the interface between aluminum and TiN or amorphous silicon is unstable that would create peeling problem.
The present invention discloses a method to prevent the undesirable metal line notching problem due to the highly reflective underlayer and/or rough topography. An aluminum nitride (AlN) layer serves as an anti-reflection layer for the aluminum metal lines. Compared with the other types of anti-reflection layer, the formation of AlN layer is easier and has less impact on the electrical properties of the IC devices according to this process.